Conventionally, various methods of detecting knocking (knock) of an internal combustion engine have been known. By way of example, a technique has been known which determines that knock has occurred when vibration intensity of an internal combustion engine is above a threshold value. It is possible, however, that noise such as vibration experienced when an intake valve or an exhaust valve is closed has intensity higher than the threshold value, while knocking does not occur. This may leads to an erroneous determination that knock has occurred, though knock has not occurred. Therefore, techniques for determining presence/absence of knocking based on vibration waveform to take into consideration characteristics other than the intensity, such as crank angle at which vibration occurs or attenuation factor have been proposed.
Japanese Patent Laying-Open No. 2003-021032 discloses a knock control device for an internal combustion engine, including a knock sensor for detecting knocking of the internal combustion engine, a statistical processing unit for statistically processing an output signal detected by the knock sensor, a first temporary determining unit for determining knock occurrence based on the result of processing by the statistical processing unit, a second temporary determining unit for determining knock occurrence based on the waveform of the output signal detected by the knock sensor, and a final knock determining unit for finally determining knock occurrence based on the temporary knock determination by the first temporary determining unit and the temporary knock determination by the second temporary determining unit. The second temporary determining unit temporarily determines occurrence of a knock based on a determination period in which the output signal output from the knock sensor is above a prescribed value, and on a maximum value of the output signal detected in the determination period. The final knock determining unit finally determines that knock has occurred, if both the first and second temporary determining units determined that knock has occurred.
Assuming that the knock occurrence is determined temporarily based on the determination period in which the output signal output from the knock sensor is above a prescribed value and on a maximum value of the output signal detected in the determination period as in the knock control device described in Japanese Patent Laying-Open No. 2003-021032, erroneous determination may be made if vibration of high intensity occurs regularly by a cause other than knocking in the internal combustion engine. Further, as the knock occurrence is determined based on the maximum value in the determination period in which the output signal output from the knock sensor is above a prescribed value, erroneous determination may be made if vibration caused not by knocking has higher vibration intensity than the vibration caused by knocking.